NAME¶

std::unordered_set::begin, - std::unordered_set::begin,

Synopsis¶

iterator begin() noexcept; (since C++11)
const_iterator begin() const noexcept; (since C++11)
const_iterator cbegin() const noexcept; (since C++11)

Returns an iterator to the first element of the unordered_set.

If the unordered_set is empty, the returned iterator will be equal to end().

range-begin-end.svg

Parameters¶

(none)

Return value¶

Iterator to the first element.

Complexity¶

Constant.

Notes¶

Because both iterator and const_iterator are constant iterators (and may in fact be
the same type), it is not possible to mutate the elements of the container through
an iterator returned by any of these member functions.

Example¶

// Run this code

#include <iostream>
#include <unordered_set>

struct Point { double x, y; };

int main() {
Point pts[3] = { {1, 0}, {2, 0}, {3, 0} };

//points is a set containing the addresses of points
std::unordered_set<Point *> points = { pts, pts + 1, pts + 2 };

//Change each y-coordinate of (i, 0) from 0 into i^2 and print the point
for(auto iter = points.begin(); iter != points.end(); ++iter){
(*iter)->y = ((*iter)->x) * ((*iter)->x); //iter is a pointer-to-Point*
std::cout << "(" << (*iter)->x << ", " << (*iter)->y << ") ";
}
std::cout << '\n';

//Now using the range-based for loop, we increase each y-coordinate by 10
for(Point * i : points) {
i->y += 10;
std::cout << "(" << i->x << ", " << i->y << ") ";
}
}

Possible output:¶

(3, 9) (1, 1) (2, 4)
(3, 19) (1, 11) (2, 14)

See also¶

end returns an iterator to the end
cend (public member function)
(C++11)
begin
cbegin returns an iterator to the beginning of a container or array
(C++11) (function template)
(C++14)